In order to solve the problems in the modeling process of an existing excitation system that a measurement safety requirement is high and test work load is large due to the fact that a traditional method for measuring a transient time-constant of a generator stator open circuit generally requires changing a circuit wiring for one time, a method for measuring the stator open circuit transient time-constant of a synchronous generator is provided. According to the method, a generator no-load simulation system is established based on a matlab/simulink platform, practically measured exciting voltage of a synchronous generator serves as input, a generator output voltage curve is simulated and obtained, a practically measured curve and the simulation curve of the output voltage of the generator are compared, and the transient time-constant of the synchronous generator stator open circuit is obtained through fitting. The measurement method combining a test and simulation fitting, the problems of complex wiring and low result accuracy of the traditional test method are effectively solved, and high economy and practical value are achieved.